Cardiac arrhythmias, and atrial fibrillation in particular, are common, dangerous medical ailments, particularly in the aging population. In patients with normal sinus rhythm, the heart, which is made up of atrial, ventricular, and excitatory conduction tissue, is electrically excited to beat in a synchronous, patterned fashion. In patients with cardiac arrhythmia, regions of cardiac tissue do not follow the synchronous beating cycle associated with the normally conductive tissue in patients with sinus rhythm. Instead, the abnormal regions of cardiac tissue aberrantly conduct to adjacent tissue, thereby disrupting the cardiac cycle into an asynchronous cardiac rhythm. Such abnormal conduction generally occurs at various, specific regions of the heart, for example: in the region of the sino-atrial (SA) node, along the conduction pathways of the atrioventricular (AV) node and the Bundle of His, or in the cardiac muscle tissue forming the walls of the ventricular and atrial cardiac chambers.
Cardiac arrhythmias, including atrial arrhythmia, may be of a multiwavelet re-entrant type, characterized by multiple asynchronous loops of electrical impulses that are scattered about the atrial chamber. These arrhythmias are often self propagating. Cardiac arrhythmias may also have a focal origin, such as when an isolated region of tissue in an atrium fires autonomously in a rapid, repetitive fashion. Cardiac arrhythmias, including atrial fibrillation, may be detected using the global technique of an electrocardiogram (EKG). More sensitive procedures of mapping the specific conduction along the cardiac chambers have also been disclosed, such as for example in U.S. Pat. No. 4,641,649 to Walinsky et al and WO 96/32897 to Desai.
A variety of clinical conditions may result from the irregular cardiac function and resulting hemodynamic abnormalities associated with atrial fibrillation, including stroke, heart failure, and other thromboembolic events. Atrial fibrillation is believed to be a significant cause of cerebral stroke; the abnormal hemodynamics in the left atrium caused by the fibrillatory wall motion precipitate the formation of thrombus within the atrial chamber. A thromboembolism is ultimately thrown off into the left ventricle, which then pumps the embolism into the cerebral circulation causing a stroke. For these reasons, there are a number of procedures for treating atrial arrhythmias.